Characterization of specific binding sites for high-density lipoproteins on rat hepatocytes: Effects of estradiol and testosterone

Abstract

Two types of binding sites for high-den;ity lipoproteins (HDL): P~ and P,_, Kd~=20 and Kd2=2.5 gg/ml, N~=130 and N2=35 ng/mg cell protein) are identified on the surface of rat hepatocytes. Conditions for predominant determination of P2 are created by employing radiolabeled lipoproteins (tasI-HDL) with a high specific activity (1000 dpm) and the differences in the kinetics of the P~-and P2-12H-HDL complex formation. P2 predominate on hepatocytes from females. The addition of estradiol to a culture of hepatocytes from males increases the content of Pv while the addition of testosterone to hepatocytes from females decreases the content of P: to the levels determined in males.

Characterization of a 95 kDa High Affinity Human High Density Lipoprotein-Binding Protein

“…A likely reason for the difference in this study is the use of a high concentration of BSA (10-20 mg/mL) during the HDL association step, which was included in order to minimize nonspecific HDL binding. Using this same high BSA concentration, we have reported a R2-HBS with N ) 200 ng/mg of cell protein in rat hepatocytes (12).…”

“…Ligand Blotting Experiments. Cell-surface-specific HDL binding has been resolved into two types of HDL-binding components with different saturation binding parameters and association/dissociation rates ( − ). Since R1-HBS was only observed with the rapid washing protocol, we modified the ligand blotting protocol by similarly decreasing the duration of the washing step to a single volume of ice-cold ligand-free solution.…”

“…The Scatchard analyses of specific 125 I-HDL 3 binding to several cell types demonstrate the existence of two families of HDL-binding sites ( − ). A high affinity family (R1-HBS) has been reported to have K d 's of 0.4-2 μg/mL and a capacity of 10−40 ng/mg of cell protein while a lower affinity family (R2-HBS) has been reported to have K d 's of 20-40 μg/mL and a capacity of 100−1000 ng/mg of cell protein.…”

“…The R1-HBS may also impact HDL retroendocytosis observed in epithelial cells and macrophages ( , ). In contrast to the lower affinity family, the R1-HBS demonstrates high ligand association and dissociation rates ( − ), the latter of which makes it difficult to detect the corresponding HBP(s) by conventional methods such as HDL−ligand blotting.…”

HDL-binding lipoproteins on human fetal hepatocytes

“…Methods for the identification of these binding sites on mt hepatocytes have been developed at the Laboratol2r of Cell and Tissue Cultures (Cardiology Research-and-Production Center). These methods are based on the isotherms for ~2SI-HDL and Scatchard plot analysis [1]. In the present study we describe two types of H DL-binding proteins that correspond to H DL-binding sites with Ko=I lng/ml (P:t) and Kd=20 ~tg/ml '(P2) on the surface of human fetal hepatocytes.…”